Re: [PATCH v3 11/23] iommufd/viommu: Add IOMMUFD_CMD_VQUEUE_ALLOC ioctl

Jason Gunthorpe
2025-05-08T12:18:31Z

On Wed, May 07, 2025 at 10:56:17PM -0700, Nicolin Chen wrote:

> What I am not sure is if the HW allows setting the ComWaitIntEn bit
> after CmdBufEn=1, which seems to be unlikely but the spec does not
> highlight. If so, this would be an modification to the HW QUEUE, in
> which case we could either do an relocation of the HW QUEUE (where
> we can set the flag in the 2nd allocation) or add an new option via
> IOMMUFD_CMD_OPTION (as Kevin suggested), and I think it should be
> a per-HW_QUEUE option since it doesn't affect other type of queues
> like Event/PRR Log Buffers.

The main question is if the control is global to the entire VIOMMU and
all its HW QUEUE's or local to a single HW QUEUE.

If it is global then some "modify viommu" operation should be used to
change it.

If it is local then some "modify hw queu" operation.

IOMMUFD_CMD_OPTION could be used with an object_id == VIOMMU as a kind
of modify..

Jason